Electrochemical cells in the form of batteries are conventionally used to power many types of electronic devices, and are available in several forms, including, for example, cylindrical, button, pouch and prismatic cells.
Prismatic cells, introduced in the early 1990s, are advantageously utilized in applications which require optimal use of space, and find application, for example, in serving as a power source for medical devices, such as Implantable Cardioverter Defibrillators (ICDs) and Cardiac Resynchronization Therapy Devices (CRT-Ds), which are implanted into a patient.
Batteries are comprised of an arrangement of alternating cell subassemblies, each subassembly including a positive electrode (cathode), a negative electrode (anode) and a separator layer interposed therebetween and also optionally between adjacent subassemblies. The electrodes may take the form of planar conductive members optionally embodied as plates, wound conductive layers, or other configurations of conductive material. In some embodiments, the anode electrode(s) of one or more subassemblies are connected in parallel to a positive current collector, and the cathode electrode(s) thereof are connected in parallel to a negative current collector. This provides combined current delivering capacity of each of the subassemblies as surface areas of interfacing surfaces (interfacial areas) of the cathode electrode(s) and anode electrode(s) are effectively summed. The output voltage is that of the individual assemblies. The current delivering capability of the cell is thus proportional to the total interfacial area between the anode and cathode subassemblies, and can be controlled by varying the footprint of the interfacial areas, for example an interfacing area of plates in a cell stack. Alternatively, subassemblies are connected in series in which case a voltage delivered is the combined voltage of each of the subassemblies with the current delivering capability being that of a given one of individual subassemblies. Thus, the voltage and current characteristics of a battery may be varied.
The capacity of a cell, which is a measure (typically in Amp-hr) of EMF potential chemically stored by the battery, is determined by the mass of active material contained in the battery, i.e., the cathode and anode material. The battery capacity represents the maximum amount of energy that can be extracted from the battery under certain specified conditions. Cell capacity is proportional to the total mass of the anode and cathode (with the appropriate coulombic balance between the two), and is determined as a function of the footprint of the interfacial area, the number of anode and cathode subassemblies, the number of plates in each subassembly, and the thickness of the anode and cathode plates.
Depending on a resultant volume of the subassemblies, for example and not limitation, a stack thickness in a prismatic battery, in achieving a battery having desired power delivering capability and power capacity, either due to changes in the number of anode or cathode plates, the thickness of the anode or cathode plates, or the total number of anode and cathode subassemblies, an overall dimension of a battery of conventional design will vary, thereby requiring battery encasements of differing size configurations.
In the field of medical implantable devices, considerable testing is required to assure that a given device meets appropriate standards for use in human beings. This is also true of the encasements of the devices, which must be constructed to ensure that the device is sufficiently well sealed and of sufficient structural integrity to implant in a person. Thus, it would be advantageous if a given encasement could be used for a variety of medical devices. However, power requirements of medical devices vary and with this variation so do the batteries vary in size. The present disclosure describes an improvement over these prior art technologies.
An implantable medical device is typically designed such that the battery powering it has an operating life, which is based on the total energy capacity, less than a design life of the other components. This is important for device reliability, as the battery longevity can be predicted rather easily, and the patient and/or physician may they be given sufficient warning before it is time to replace the device by the device sensing the remaining energy of the battery. If the device were designed such that the battery could potentially outlast any of the other components, such a warning to the patient and/or physician might be difficult.
Frequently a medical device will be produced in different models, all being assembled from the same primary components, but with each having a different set of features. Sometimes the different feature sets will consume the device battery capacity at substantially different rates (power), resulting in significant differences in the longevity of the different models. In those situations, the battery energy capacity needs to be chosen to deliver the desired longevity in the highest cases of power consumption. In extreme cases, the differences in longevity may be so great that it is desired to provide different battery capacities in the different models, so that the longevity of the battery in the longest lasting model will not exceed the design life of any of the other device components. It is also possible that the varying power consumption of different models may require batteries of different power capability. Typically when either of these situations occur, the different batteries occupy different volumes, requiring changes in the overall device mechanical design. As components are no longer shared between device models, component costs and device costs rise. As such, it is desirable to develop a family of batteries, all using the same outer case, but with varying power and capacity.